A Comparison of the Apical Extrusion of Debris during the Preparation of Root Canal with Medin, RaCe, and ProTaper Rotary Systems

Statement of the Problem: The extrusion of intracanal debris is one of the challenging problems related to almost all root canal preparation systems, which may cause flare-ups and impairment in the healing process. Purpose: This study was conducted to evaluate the amount of apically-extruded debris during root canal preparation using Medin (MEDIN Co., Czech Republic) rotary system compared with two common rotary systems, including ProTaper (Dentsply Maillefer., Switzerland) and RaCe (FKG Dentaire, Switzerland). Materials and Method: In this in vitro study, Sixty mandibular premolars with single canal were randomly assigned to three groups (n=20). The root canals were prepared with Medin, ProTaper, and RaCe rotary instruments based on their manufacturers’ instructions. The debris were collected into pre-weighted Eppendorf tubes. The weight of the extruded debris was calculated by subtracting the pretreatment weight of the vials. Data were analyzed using the Kruskal-Wallis test at a 5% significance level. Results: Medin instrument caused significantly less debris extrusion in comparison with ProTaper and RaCe (p< 0.05). The differences between the ProTaper and RaCe rotary systems were not statistically significant (p= 0.752). Conclusion: Within the limitations of this in vitro study, Medin rotary system produced less apical extrusion than ProTaper and RaCe.


Introduction
The importance of mechanical root canal preparation has persuaded manufacturers to introduce endodontic rotary files with different design features, kinematics, and advantages [1]. One of the frustrating problems related to almost all root canal preparation systems, which may cause flare-ups and affect the healing process is the debris extrusion [2][3].
Medin (MEDIN Co., Czech Republic) rotary files with inactive tips and a three-bladed profile are designed to shape curved canals using the crown-down technique. The manufacturers claim that the resistance of files to cyclic fatigue increases by special heat treatment processing. Several Studies have compared this rotary system with popular rotary systems in terms of shaping abilities. Bidar et al. [4] microscopically compared the cleaning efficiency of this rotary system with RaCe and Mtwo instruments and did not find any differences between the groups. In another study, Moradi et al. [5] compared the dentin removal and centering ability of these three rotary file systems in curved canals and found that Mtwo is more conservative for root canal preparation. Talati et al. [6]   in the canal until the tip end was seen in the apical foramen. The working length was recorded as 1 mm short of this length. The length of all the roots were standardized by removing the excess coronal reference points perpendicular to the long axis. The extrusion debris test was performed based on the method proposed by Montgomery and Meyers with some modifications [11]. The samples were randomly sorted into three groups (n=20) and marked. The root surfaces were covered with a Teflon band, except for 1 mm in the apical part. The teeth were then placed in holes created in the center of the cap of the Eppendorf tubes and fixed at the cementoenamel junction. Sixty Eppendorf tubes without caps were weighted three times to 10 -4 g precision using a digital scale (GT300, A&D Company, Japan). The mean value of these consecutive measurements was recorded for each tube. The apical part of the roots was positioned inside the Eppendorf tubes and sealed by cyanoacrylate adhesive. In order to balance the air pressure inside and outside of the tube, a 25-gauge needle was inserted and secured in caps by the side of each tooth. The whole assembly was secured in a brown glass to prevent any movement during cleaning and shaping procedures.

Root canal preparation
All the root canal preparations were done by one expert operator using new files. After every three pecking movements, the root canals were irrigated with 2 ml of distilled water. The debris on the files was wiped off by  Table 1 shows the mean and standard deviation of the amount of apically extruded debris for each group. According to Table 1

Discussion
Several laboratory studies have been conducted to eval-  [10,[12][13]. Apart from the S files, the ProTaper files. The term Pitch has been applied to the distance between the edges of two cutting blades measured along the working part of an instrument [16][17].
The length of pitch can change the mechanical properties of rotary files; a study performed by Burklein et al. [17] showed that the files with shorter pitch had greater contact area with root canal walls and thereby caused more torsional stress during instrumentation. In another The amount of debris extrusion also depends on instrument type, size, and working length [19][20] by absorbing some debris. These media were therefore not used in this study [21][22].
To prevent the probability of crystallization of common irrigants, such as sodium hypochlorite in the collection tube, distilled water was used as irrigant during the preparation [22].
The present findings are restricted to teeth with mature apices and cannot be extrapolated to teeth with open apices. There are some non-standardizable factors, such as dentin micro-hardness in human teeth models, which may influence the amount of apical extrusion [2]; however, considering possible adverse effects related to simulated acrylic blocks, such as the effect of heat on the hardness of resin material, made us use human teeth models in this study.

Conclusion
Within the limitations of this in vitro study, the findings showed that, during canal preparation, Medin rotary systems produced less apical extrusion of debris compared to ProTaper and RaCe rotary systems.